1. Field of Invention
This invention relates to low power broadcasting under FCC Part 15 Rules, specifically to leveraging low power commercial (AM and FM) band re-broadcasting of specialized frequencies outside commercial bands (such as aircraft communications) using single or multiple distributed low power transmitters with overlapping areas of coverage.
2. Prior Art
Individuals viewing airport operations are unable to listen to the aircraft and traffic control communications that would make observation more informative and enjoyable; since these communications occur at frequencies 108-136 MHz which are well out of range of personal and car radios. The inability to easily listen to such communications is a roadblock to participation in General Aviation and presents a barrier, perceived and unperceived, that aviation in general is expensive and exclusive.
In order to overcome this barrier, the interested individual must first a) obtain the proper (and relatively costly) specialized receiver and then b) be educated in the frequencies of operation at the given airport. An alternative to circumvent this barrier is a capability that will receive and re-broadcast such aircraft communications on readily accessible commercial (AM and FM) bands.
Receiving followed by retransmitting has taken a myriad of forms in the prior art, but none combine low power transmitter operation, integral station identification messages, and a fixed installation such as at an airport. Many such instances of the prior art concern themselves with cellular phone operations, satellite operations, TV audio conversion, and general down conversion of electromagnetic signals. As listening to two way aircraft and air traffic control signals is obviously a simplex (one way) channel with respect to the listener (the spectator rightly cannot participate in any aircraft-ATC conversations), much of this prior art does not apply as it is concerned with duplex (two way) transmissions.
U.S. Pat. No. 5,812,086 to Bertiger et al. (1998) concerns retransmission (both simplex and duplex) of geo-location signals that involves calculation of a geographical location as well as an ‘infrastructure transceiver apparatus’ such as a satellite host. U.S. Pat. No. 5,784,028 to Corman (1998) is simplex, but focuses on geo-location to obstructed areas. U.S. Pat. No. 5,508,731, issued to Kohorn (1996) uses a plurality of ‘remote receiving stations’ to conduct gaming and evaluation of television programming, so is duplex, but is not low power, is not focused on re-broadcasting strictly for the listening enjoyment of the user, and does not store station identification in the claimed local memory. U.S. Pat. No. 5,434,565 issued to Simon et al. (1995) rebroadcasts aircraft weather information, but not on commercial frequencies (it uses the common air traffic frequencies or CTAF frequencies) and does not employ multiple low power transmitters. U.S. Pat. No. 5,265,024 issued to Crabill et al. (1993) is also similar in scope.
U.S. Pat. No. 4,905,303 issued to Johnson et al. (1990) consists of a small device to down convert the audio from television broadcasts to AM or FM frequencies, this device to be attached to the AM/FM receiver in question. This implementation is not a fixed, low power transmitter or set of spatially fixed low power transmitters, does not involve aircraft communications, contains no station identification, multiplexing, or other sophisticated capability, and has in recent years simply been superseded by FM tuners that extend up into the TV broadcast spectrum (at least for TV channels in the range of 2-10). U.S. Pat. No. 5,173,775 issued to Walker (1992) entails receiving and demodulating a television signal for re-broadcast in a possibly different modulation scheme, and is not low power. U.S. Pat. No. 5,418,577, issued to Bagley (1995) is for rebroadcast of TV audio on FM channels, as in a residence or small home theater. This issuance is presumably low power, but has no multiplicity of low power transmitters, requires no specialized receiver (only a television), has no station identification capability, no timer or multiplexer function for multiple channels, and does not deal explicitly with aircraft communications or AM modulation embodiments. U.S. Pat. No. 5,628,056, issued to Grysiewicz et al., is similar and contains transmission of TV audio to AM as well as FM receivers. Again, this invention is not explicitly low power, does not explicitly contain a plurality of low power transmitters, and does not receive specialized (non commercial band) transmissions or broadcast a station identification message.
U.S. Pat. No. 4,541,119, issued to Cooper et al. (1985) describes a low power AM transmitter that is used as a portable advertising and public awareness node placed in a portable sign. This patent also references some other instances of ‘serial’ or ‘daisy chained’ low power transmitters, but none are a plurality of spatially fixed low power transmitters, none involve aircraft communications (only radio or public awareness messages), none broadcast a station identification, and all are arcane in their technological implementation (transmitters spaced at 3 m intervals, signals to the low power transmitters conveyed by wires between low power transmitters and tape recorders, and the like).
Richardson discloses a duplex AM/FM rebroadcast system in U.S. Pat. No. 4,353,127 (1982), but this system is not explicitly low power and does not contain a plurality of low power transmitters, a storage area for station identification or other stored messages, a timer/multiplexer for considering multiple specialized frequencies, a specialized receiver, or an input mechanism for a storage area and recorded messages.
U.S. Pat. No. 5,867,794 issued to Hayes et al. (1999) is concerned with rebroadcast of portable (cellular) telephone audio to an automobile's AM/FM radio and thus is presumably low power but is implicitly confined to the region of the interior of a vehicle, since it is obviously undesirable to broadcast individual telephone conversations to the general public.
U.S. Pat. No. 6,725,035 to Jochim et al. (2002) is concerned with cellular telephone transmissions and rebroadcasts to aircraft, as is U.S. Pat. No. 6,650,898 (also to Jochim). U.S. Pat. No. 5,915,210 issued to Cameron et al. (1999) uses a plurality of transmitters and a plurality of carriers, but also incorporates satellite communications and is not explicitly low power. U.S. Pat. No. 5,726,786 to Heflinger (1998) uses a plurality of transmitters and receivers but concerns an all-optical network. U.S. Pat. No. 5,038,402 to Robbins is concerned with digital transmission and reception of high quality audio in the FM band, but aircraft communications are neither high quality nor digital in nature. This disclosure also does not involve low power transmission or a plurality of such low power transmitters.
U.S. Pat. No. 4,232,392 issued to French (1980) uses a plurality of similar transmitters to overcome distortion effects in systems where a receiver receives signals from two nearly equal power transmitters simultaneously. A feature of this patent is that the system transmits all messages at least twice—something that would obviously be detrimental for providing aircraft communications to spectators.
Various patents (U.S. Pat. Nos. 6,836,650; 6,813,485; 5,263,196) describe frequency down conversion (AM to FM, FM to AM, either to other types of modulation), which can be viable mechanisms for converting aircraft communications (which are AM or amplitude modulated) signals, but are ancillary to retransmission and are ultimately only a partial implementation of multiple steps required for providing aircraft communications to the public on commercial radio bands.
Simply put, the prior art does not contain a radio device that can legally, cost effectively, and capably broadcast aircraft communications to the general public on commercial radio bands. All are deficient in at least one of the following required features:                a. a specialized receiver and antenna in a fixed location (at an airport);        b. one or more low power transmitter(s) and antenna(s) in a fixed location, with sufficient signal coverage for the area that intended spectators will occupy;        c. a periodic and repeatable means for identifying the frequency and location of the FCC Part 15 low power transmitters;        d. a timer/multiplexer to prioritize specialized frequencies, cue the station identification message required by the FCC Part 15 low power rules at required intervals, and regulate other minor points of operation;        e. a storage location for the station identification message and transmitter and receiver configuration parameters;        f. and an input mechanism for entering and storing the station identification message, receiver and transmitter configuration parameters, and other control and sequencing data;        g. sufficient signage to make the public aware of the capability to listen to aircraft communications on commercial bands.        